ARLINGTON, Va. -- Anti-war activist Cindy Sheehan on Monday moved another step -- actually several thousand of them -- toward carrying out her promise to run against House Speaker Nancy Pelosi because the California Democrat won't consider impeachment proceedings against President Bush.

Sheehan and about 200 other war protesters began walking from Arlington National Cemetery to the Capitol Hill office of Rep. John Conyers, chairman of the House Judiciary Committee, where any impeachment proceedings would begin. Sheehan said she would ask Conyers to initiate impeachment proceedings against both Bush and Vice President Dick Cheney.

"Impeachment is not a fringe movement, it is mandated in our Constitution; Nancy Pelosi had no authority to take it off the table, " Sheehan told her group of orange-clad activists Monday. "If Nancy Pelosi doesn't do her constitutionally mandated job by midnight ... I will announce that I'm going to run against her."

Across the street, about 20 people demonstrated against Sheehan and the other anti-war protesters.

Sheehan, whose 24-year-old son Casey was killed in Iraq, has been saying for two weeks that she would seek to oust Pelosi from office by running against her as an independent in her San Francisco district if Pelosi didn't change her mind by July 23 on trying to impeach Bush.

Conyers, D-Mich., introduced a bill last term calling on Congress to determine whether there are grounds for impeaching Bush. Pelosi has steadfastly dismissed any talk of impeachment, saying Democrats should focus their efforts on ending the war in Iraq.